[GRASS-user] Thiessen Polygons

[Milton Cezar Ribeiro]

Dear Glynn Clements
Is there a command r.grow.distance on GRASS?
I tryed to find it on Native WinGrass, but it appears not be available,
almost on 6.3 version.

Best wishes

miltinho

2009/2/14 Glynn Clements <glynn at gclements.plus.com>

>
> Jan Hartmann wrote:
>
> > With that in mind, if the algorithm you propose would be indeed an
> > approximation to weighted Voronoi polygons, *and* it wouldn't be all to
> > hard to implement (I have no idea about that), would it make sense to
> > propose this as a new RFC for GRASS?
>
> Oops; I spoke too soon.
>
> In retrospect, this won't work. r.grow.distance relies upon the fact
> that once a cell falls out of consideration, it stays out. It will
> only consider cells which either are from the current row, or were
> used on the previous row.
>
> With distance scaling, this doesn't hold. A cell could be temporarily
> overriden by much nearer cells with increased scale factors (lower
> weights), then regain its influence once the distance increases.
>
> IOW, this isn't something which can implemented given the algorithm
> used by r.grow.distance. Any algorithm which implemented distance
> scaling would inevitably have worst-case memory usage proportional to
> the number of non-null input cells, as you can never "forget" a cell
> whose scale factor is lower than those currently being considered, as
> it will eventually regain its influence.
>
> --
> Glynn Clements <glynn at gclements.plus.com>
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